#!/usr/bin/env bash
#
# setup-host.sh -- set a host's name (per the Network Domain Name Schema) and
# install the shared SSH MOTD banner. Works on Alpine, Debian, and Alma via
# oslib.sh.
#
# Hostnames follow globals/Network Domain Name Schema.md. Our VMs skip the
# region code and use srvno.de as the base, so the form is:
#       <service>-<n>.srvno.de        e.g. sto-1.srvno.de
# from which we derive:
#       Node ID = <SERVICE>-<N>       e.g. STO-1   (short name, uppercased)
#
# The MOTD is rendered from globals/motd.txt. You edit the *content* there;
# this script draws the borders and computes every bit of padding, so the box
# stays aligned regardless of value length (the spacing problem, solved).
#
# Usage:
#   bash setup-host.sh sto-1                 # -> sto-1.srvno.de, Node ID STO-1
#   HOST=dns-1 bash setup-host.sh
#   HOST=web-2.srvno.de bash setup-host.sh   # full FQDN accepted too
#   BASE_DOMAIN=example.net HOST=app-1 bash setup-host.sh
#   DATACENTER="Stockholm SE" HOST=sto-1 bash setup-host.sh
#
# Env:
#   HOST          required   short name (sto-1) or FQDN (sto-1.srvno.de)
#   BASE_DOMAIN   srvno.de   appended when HOST has no dot
#   DATACENTER    "Globally Everywhere"   shown in the MOTD
#   MOTD_TEMPLATE <repo>/globals/motd.txt
#   MOTD_WIDTH    60         inner width of the MOTD box
#   SET_HOSTNAME  1          set to 0 to render MOTD only (skip hostname)

set -euo pipefail

REPO_ROOT="$(cd "$(dirname "${BASH_SOURCE[0]}")/.." && pwd)"
# shellcheck source=scripts/oslib.sh
. "$REPO_ROOT/scripts/oslib.sh"

: "${HOST:=${1:-}}"
: "${BASE_DOMAIN:=srvno.de}"
: "${DATACENTER:=Globally Everywhere}"
: "${MOTD_TEMPLATE:=$REPO_ROOT/globals/motd.txt}"
: "${MOTD_WIDTH:=60}"
: "${MOTD_OUT:=/etc/motd}"
: "${SET_HOSTNAME:=1}"

[[ $EUID -eq 0 ]] || _die "Run as root."
[[ -n "$HOST" ]] || _die "Set HOST=<service>-<n> (e.g. sto-1) or a full FQDN."
os_detect

# ----------------------------------------------------------------------------
# Derive FQDN / short name / Node ID from HOST
# ----------------------------------------------------------------------------
if [[ "$HOST" == *.* ]]; then
    FQDN="$HOST"; SHORT="${HOST%%.*}"
else
    SHORT="$HOST"; FQDN="$HOST.$BASE_DOMAIN"
fi
NODE_ID="$(printf '%s' "$SHORT" | tr '[:lower:]' '[:upper:]')"

# Light sanity check against the schema (svc code + instance number). Warn
# only -- we don't want to block an intentional exception.
[[ "$SHORT" =~ ^[a-z]{2,4}-[0-9]+$ ]] \
    || _warn "Short name '$SHORT' doesn't match <svc>-<n> (see globals/Network Domain Name Schema.md)."

_log "Host:      $FQDN"
_log "Node ID:   $NODE_ID"
_log "Data Cntr: $DATACENTER"

# ----------------------------------------------------------------------------
# Set hostname (OS-gated inside oslib)
# ----------------------------------------------------------------------------
if [[ "$SET_HOSTNAME" == "1" ]]; then
    _log "Setting hostname to $FQDN ..."
    set_hostname "$FQDN"
fi

# ============================================================================
# MOTD renderer
# ============================================================================
# All padding is computed in ASCII (spaces, labels, values are ASCII so
# ${#str} is the column count). Box-drawing glyphs are only ever emitted by
# repetition, never measured -- so this is correct under any shell/locale.

W="$MOTD_WIDTH"

_spaces() { printf '%*s' "$1" ''; }                       # N ASCII spaces
_repeat() { local i; for ((i=0;i<$2;i++)); do printf '%s' "$1"; done; }  # glyph xN

# Bordered content line: ┃ + <inner W cols> + ┃
_line() { printf '┃%s┃\n' "$1"; }

# Center an ASCII string within W.
_center() {
    local s="$1" len=${#1} pad left
    (( len > W )) && { s="${s:0:W}"; len=$W; }
    pad=$(( W - len )); left=$(( pad / 2 ))
    _line "$(_spaces "$left")$s$(_spaces $(( pad - left )))"
}

# Center a pre-built string of KNOWN visible width vis (may contain glyphs).
_center_known() {
    local s="$1" vis="$2" pad left
    pad=$(( W - vis )); left=$(( pad / 2 ))
    _line "$(_spaces "$left")$s$(_spaces $(( pad - left )))"
}

# Field line: left margin, right-aligned label, ": ", value, pad to W.
LM=8           # left margin before the label column
_field() {
    local label="$1" value="$2" content
    content="$(printf '%*s%*s: %s' "$LM" '' "$LABELW" "$label" "$value")"
    local len=${#content}
    (( len > W )) && { content="${content:0:W}"; len=$W; }
    _line "$content$(_spaces $(( W - len )))"
}

# Mini double-line box around centered ASCII text, itself centered in W.
_inner_box() {
    local text="$1" tw=$(( ${#1} + 2 )) vis
    vis=$(( tw + 2 ))                       # ║ + text(+2 spaces) + ║
    _center_known "╔$(_repeat '═' "$tw")╗" "$vis"
    _center_known "║ $text ║" "$vis"
    _center_known "╚$(_repeat '═' "$tw")╝" "$vis"
}

render_motd() {
    # First pass: compute LABELW (max @F@ label width) so colons align.
    LABELW=0
    local line tok rest label
    while IFS= read -r line || [[ -n "$line" ]]; do
        [[ "$line" =~ ^[[:space:]]*# ]] && continue
        [[ "$line" == "@F@ "* ]] || continue
        rest="${line#@F@ }"; label="${rest%%|*}"
        (( ${#label} > LABELW )) && LABELW=${#label}
    done < "$MOTD_TEMPLATE"

    # Second pass: emit. Borders come from the @TOP@/@HR@/@BOT@ tokens.
    while IFS= read -r line || [[ -n "$line" ]]; do
        [[ "$line" =~ ^[[:space:]]*# ]] && continue
        [[ -z "$line" ]] && continue
        tok="${line%% *}"; rest="${line#"$tok"}"; rest="${rest# }"
        # substitute placeholders
        rest="${rest//\{\{HOSTNAME\}\}/$FQDN}"
        rest="${rest//\{\{NODE_ID\}\}/$NODE_ID}"
        rest="${rest//\{\{DATACENTER\}\}/$DATACENTER}"
        case "$tok" in
            @TOP@)   printf '┏%s┓\n' "$(_repeat '━' "$W")" ;;
            @BOT@)   printf '┗%s┛\n' "$(_repeat '━' "$W")" ;;
            @HR@)    printf '┣%s┫\n' "$(_repeat '━' "$W")" ;;
            @BLANK@) _line "$(_spaces "$W")" ;;
            @C@)     _center "$rest" ;;
            @BOX@)   _inner_box "$rest" ;;
            @F@)     _field "${rest%%|*}" "${rest#*|}" ;;
            *)       _warn "Unknown MOTD token: $tok (skipped)" ;;
        esac
    done < "$MOTD_TEMPLATE"
}

[[ -f "$MOTD_TEMPLATE" ]] || _die "MOTD template not found: $MOTD_TEMPLATE"
_log "Rendering MOTD -> $MOTD_OUT"
render_motd > "$MOTD_OUT"
chmod 644 "$MOTD_OUT" 2>/dev/null || true

_log "Done."
echo
cat "$MOTD_OUT"